Radio-frequency (RF) devices are widely used in communication systems. Various RF devices that operate at high frequencies, for example, in GHz frequency ranges, need to be integrated with other devices to form a system. Therefore, the RF devices need to be packaged in package structures.
There are several types of conventional package structures used for packaging the RF devices. In a first package structure, RF devices are formed in a device die that is stacked on a package substrate. The package substrate is further bonded to a printed circuit board (PCB) through flip-chip bonding. Bond wires are used to provide DC power to the device die, and to transmit RF signals between the device die and the package substrate. The RF signals are further transmitted to the PCB through through-package vias that are formed in the package substrate. In these package structures, the bond wires are typically very long compared to the wavelengths of the RF signals, and the RF loss on the bond wires is high. Furthermore, the formation of the bond wires may cause electro-static discharge (ESD) that damages the RF devices. The device die and the package substrate may also have a high mismatch in coefficient of thermal expansion (CTE), and hence there may be high stresses generated in the device die.
In another one of conventional packages, RF devices are formed in a device die, wherein the device die is bonded to an interposer through a flip chip package. The interposer is stacked on a package substrate. The package substrate is further bonded to a PCB through flip-chip bonding. Bond wires are used to bond the interposer to the package substrate. The bond wires are used to provide DC power to the device die through the interposer, and to transmit RF signals between the device die and the package substrate. The RF signals are further transmitted to the PCB through through-package vias that are formed in the package substrate. Again, in these package structures, the bond wires are long compared to the wavelengths of the RF signals, and the RF loss on the bond wires is high. Furthermore, the formation of the bond wires may also cause the ESD, which damages the RF devices.